Knowing the weight of concrete is part of any building project. Building codes state the maximum loads for all types of buildings, from skyscrapers to residential buildings. Concrete is a type of "dead load." A dead load is fixed in the building and cannot be moved. Because dead loads are inherent of the structure of the building and cannot be removed afterward, it's vital to calculate the weight of concrete correctly.
Determine the nominal weight for a cubic foot of your concrete. For residential concrete, the industry standard nominal weight is 68 Kilogram per cubic foot.
Measure the length of the slab. For example, one side of an old patio might be 10 feet.
Measure the width of the slab. For example, the other side of the patio might be 6 feet.
Determine the depth of your slab. For residential patio and walkways, the depth is 4 inches (1/3 foot). If you're not sure, dig a small hole right next to the patio and measure from the top surface to where the concrete ends in the ground.
Multiply your answers from Steps 2, 3 and 4 together to find your cubic volume: 10 feet x 6 feet x 1/3 foot = 20 cubic feet.
Multiply your answer to Step 5 by the weight you determined in Step 1: 20 cubic feet x 68 Kilogram per cubic foot = 1361 Kilogram of concrete for your 10-by-8 patio.
If you have unusually light concrete, like the concrete used for decking, then look on the packaging to determine the weight.